1. Field of the Invention
This invention is related in general to the field of orthopedic devices and methods for joining fractured bones. In particulars the invention provides an improved pin-type bone-clamping device and an installation tool that permit the quick joining of fractured bones.
2. Description of the Related Art
When bones are either fractured by accident or severed by surgical procedure, the healing process requires that they be rejoined and kept together for lengthy periods of time in order to permit the recalcification and bonding of the severed parts. Accordingly, adjoining parts of a severed or fractured bone are typically clamped together or attached to one another by means of a pin or a screw driven through the rejoined parts. Movement of the pertinent part of the body is then kept at a minimum by a cast, brace or splint in order to promote healing and avoid mechanical stresses that may cause the bone parts to come apart during normal or necessary bodily activity.
The surgical procedure of attaching two or more parts of a bone with a pin-like device requires an incision in the tissue surrounding the bone and the drilling of a hole through the bone parts to be joined, often with little space to operate without inflicting further injury to the patient. Therefore, it is very important that the bone-clamp device used be capable of quick installation with a simple procedure. U.S. Pat. No. 4,796,612 (1988) and No. 4,903,692 (1990) to Reese describe a bone clamp and a corresponding installation tool that enable a surgeon to easily drive a pin through an aperture in two or more parts of a bone and lock it in place by means of a self-locking button placed around the shaft of the pin. The tip of the pin has a hook that engages the back surface of the bone after protruding through the aperture in the bone. The shaft of the pin features circumferential notches that engage the button in ratchet fashion, so that the button can be pushed against the front surface of the bone to anchor the pin in place, thereby clamping the severed bone parts together. The installation tool consists of a syringe-like structure comprising an outer barrel and a slidably-disposed hollow inner piston wherein the shaft of the pin is mounted prior to application. A retaining fork projecting inwardly from the distal and inside surface of the barrel engages the notches on the shaft of the pin and prevents the pin from moving freely in relation to the barrel. Through a longitudinal groove in which the retaining fork is slotted, the piston is free to slide inside the barrel and engage the button, which can thus be pushed forward along the shaft of the pin while the pin is held by the retaining fork so that the button is locked in place against the surface of the bone.
The Reese bone clamp and installation tool provide an efficient method for clamping fractured bones together, but the retaining fork mechanism described in U.S. Pat. No. 4,903,692 for coupling the pin to the barrel of the installation tool has been found to be unsatisfactory at times when relatively great pressure is required to push the self-locking button forward. This invention is directed at solving this problem by describing an improved coupling mechanism between the pin and the tool.